This proposal will result in bioabsorbable brachytherapy devices for the treatment of localized primary cancers and treatment of tumor beds after tumor removal. This approach develops an entirely new brachytherapy method using absorbable support matrices and chelated radionuclides. The bioabsorbable brachytherapy materials can replace conventional permanently embedded metal sources in primary tumors, and may be of particular use following surgical removal of localized tumors. The brachytherapy materials will provide highly localized radiation therapy and the bioabsorbable matrix materials eliminate the need for follow-up procedures to recover the sources, as is currently done. In PhaseII of the grant, we will develop radiolabeling parameters and evaluate bioabsorbable brachytherapy devices in vitro and in vivo in limited animal studies to establish stability and safety. In Phase II, animal models of human breast and prostate cancer will be used to establish efficacy as a prelude to testing in humans. PROPOSED COMMERCIAL APPLICATIONS: A biosorbable brachytherapy device can be used for treatment of localized primary cancers and treatment of tumor beds after tumor removal.